Each component of the electric generator has an upper-limit temperature, and therefore measures are taken to prevent temperature of each component from exceeding the upper-limit temperature during the operation of the electric generator by modification of an arrangement of each component or by forcibly circulating an atmosphere around each component. With respect to modification of the arrangement, A rise in temperature caused by an atmosphere temperature or caused by the self-heating of a component is restrained, for example, by disposing the component at a place at which the component comes into contact with outer air as easily as possible so as to be easily cooled. In a forced air circulation method, a cooling effect is obtained, for example, by disposing an air-circulating fan in a housing of the electric generator and by allowing the fan to supply air to a component that is intended to be restrained from rising in temperature.
Patent Literature 1 discloses a power generation control device for use in vehicles that includes a generator temperature estimating means that estimates the temperature of an attention-focused part of the electric generator based on the temperature of an electric generator, based on the number of rotations of the electric generator, and based on the exciting current of the electric generator and an amount-of-power generation limiting means that limits the amount of power generation when the temperature of the attention-focused part estimated by the generator temperature estimating means exceeds an upper limit value.